Polyamide feed yarn for false-twist texturing, process of false-twist texturing, and product thereof

ABSTRACT

A polyhexamethylenedodecanedioamide feed yarn for false-twist texturing has excellent performance when draw-textured at a draw ratio of 3.5X to 4.5X, an applied twist of 170 to 200 turns per inch and a texturing temperature of 150* to 200*C. The textured product is strong, has a low yarn-on-yarn friction and high values for crimps per inch, crimp elongation and ratio of crimps per inch to turns per inch. Triclinic X-ray diffraction patterns show a marked increase in the Alpha -crystalline form during texturing.

it tts tt aliga et a1. Jan. 7, 1975 POLYAMHDE FEED YARN FOR 9 3,418,199 12/1968 Anton et a1 161/173 x FALSEJEWIST TEXTURING, PROCESS 1: 3,560,448 2/1971 Lodge 260/78 R 3,608,299 9/1971 Dugas 57/157 TS FALSE'TWIST TEXTURING AND 3,696,074 10/1972 Tsuda et a]. 260/78 R PRODUCT THEREOF [75] Inventors: Janardhana B. Baliga, Newark,

De1.; Robert L. Dainton, Boothwyn, Primary Examiner-John Petrakes: Pa.

[73] Assignee: E. 1. du Pont de Nemours and Company, Wilmington, Del. [57] ABSTRACT [22] Filed: July 2, 1973 A polyhexamethylenedodecanedioamide feed yarn for [21] Appl' 375341 false-twist texturing has excellent performance when draw-textured at a draw ratio of 35X to 4.5X, an ap- [52] U.S. Cl. 57/140 R, 57/157 TS, 260/78 R plied twist of 170 to 200 turns per inch and a texturing [51] Int. Cl. D02g 1/02, D02g 3/02, D02g 3/24 temperature of 150 to 200C. The textured product is [58] Field 011 Search 57/140 R, 34 HS, 157 TS; strong, has a low yarn-on-yarn friction and high values 264/168,290; 161/172,173;260/78 R,78 A, for crimps per inch, crimp elongation and ratio of 78 S crimps per inch to turns per inch. Triclinic X-ray diffraction patterns show a marked increase in the [56] References Cited tit-crystalline form during texturing.

UNITED STATES PATENTS 3,184,436 5/1965 Magat 260/78 R 5 Claims, 3 Drawing Figures Patented Jan. 7, 1975 2 Sheets-Sheet l Patented Jan. 7, 1975 2 Sheets-Sheet 2 FIG- FOLYAMIIDE FEED YARN IFOIR FALSE-TWIST TEXTURIING, PROCESS OF FALSE-TWIST TEXTURING, AND PRODUCT THEREOF BACKGROUND OF THE INVENTION This invention relates to textured polyamide yarn and its production, and is more particularly concerned with a novel feed yarn, a process for draw-texturing it and a novel textured yarn suitable for knitting stretch fab- IICS.

The polyamide yarns of commerce are of 6-6 nylon (polyhexamethyleneadipamide) or 6-nylon (from A-amino-caproic acid or caprolactam). Only minor amounts of yarns are manufactured from other polyamides, such as ones having branched chains or aromatic groups in the chains. A vast number of other polyamides are possible, but previous extensive research had not found any as desirable as 66 nylon for textile yarn, even among the linear aliphatic polyamides most closely related to 66 nylon. It is surprising, therefore, to find that one can be prepared to have properties superior to 6-6 nylon yarn, particularly for textile uses where texturing is important to provide bulk, softness and stretch in fabrics.

SUMMARY OF THE INVENTION The present invention provides a polyamide feed yarn for drawing and texturing into products which are superior to comparable 6-6 nylon yarn for textile uses. The invention also provides a draw-texturing process for providing improved crimp properties. An improved textured yarn is provided which has tenacity and modulus properties at least equivalent to comparable 6-6 nylon yarn under normal conditions and is less sensitive to humidity, which has improved ratios of crimp to turns per inch of twist liveliness for better processibility when knitting, and which can be knitted into more powerful stretch fabrics having better recovery from stretching. Other advantages of the invention will appear hereinafter.

The polyamide feed yarn of this invention has a break tenacity of at least 6.5 grams per denier and a yarn-nyarn coefficient of friction'of less than 0.50 which is free from stick-slip behavior when tested as described Subsequently. The polyamide consists essentially of polyhexamethylenedodecanedioamide of 30 to 70 relative viscosity having a triclinic crystallite cell structure characterized by a crystal perfection index of less than 50 percent with substantial freedom from the a-crystalline form. The yarn is preferably an undrawn yarn suitable for drawing at a draw ratio of 3.5X to 4.5X when the yarn is textured. However, the yarn can be partially drawn or fully drawn prior to the the texturing opera tion. Yarn which has been drawn to have a break elongation of about 30 to 40 percent is usually used in conventional texturing operations.

In a preferred'process of this invention for drawing and false-twist texturing hosiery yarn, undrawn feed yarn of 30 to 70 relative viscosity polyhexamethylenedodecanedioamide, having a triclinic crystallite cell structure characterized by a crystal perfection index of less than 50 percent with substantial freedom from the a-crystalline form, is draw-textured at an applied twist of I70 to 200 turns per inch and a texturing temperature of 150 to 200C. The draw-texturing can be performed in three ways. In the tandem process, drawing is completed in a separated draw zone and the drawn yarn is immediately fed into a false-twist texturing zone. In the simultaneous process, drawing is accomplished in the false-twist texturing zone. In the third proces, part of the drawing is accomplished in a separate draw zone and drawing is completed in the falsetwist texturing zone.

Textured polyamide yarn is readily produced which has a break tenacity of at least 6.5 grams per denier, a yarn-on-yarn coefficient of friction of less than 0.50, free from stick-slip behavior, about 45 to crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off pirn) of at least 1.6; the polyamide consisting of polyhexamethylenedodecanedioamide of 30 to relative viscosity having a triclinic cell structure characterized by a crystal perfection index of at least percent and a ratio of a/B crystalline forms of at least 1.0. The excellent crimp properties obtained are believed to be due, at least in part, to the change in triclinic cell structure which occurs during texturing. Accordingly, the feed yarn is produced under conditions which provide a crystal perfection index of less than 50 percent and substantial freedom from the a-crystalline form, and heating of the feed yarn prior to the drawtexturing operation is avoided.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are schematic representations of pre ferred apparatus for practicing the draw-texturing process. FIG. 1 illustrates a coupled drawing and texturing operation and FIG. 2 illustrates simultaneous drawtexturing operation.

FIG. 3 is a side view of a friction-twist device for imparting twist to yarn during draw-texturing. Orientation relative to yarn travel is indicated.

DETAILED DESCRIPTION FIGS. 1 and 2 represent single positions of a drawtwister rngdified to both cold-draw and false-twist texture a drawable nylon feed yarn. Corresponding parts are identically numbered. Drawable feed yarn 12 is preferably completely undrawn and fed directly from its partially shown spin bobbin 10. Via creel pigtail guide 14, creel snub guide 16, and traverse guide 18, yarn 12 is led to and partly around cott roll 20 before passing through the nip between cott roll 20 and driven feed roll 22.

Draw roll 26 is driven and comprises two sections: (1) minor step 30 serving as a first drawing stage, and (2) major step 28 serving as a second drawing stage. Separator roll 32 is also provided, as is well understood. From feed roll 22, yarn 12 first passes about draw pin 24 and then to several wraps around minor step 30 and separator roll 32. Because the peripheral velocity of minor step 30 is greater than that of feed roll 22, yarn 12 becomes drawn.

Yarn 12 next passes in contact with hot plate 34 (or other known heating means) which is sized and operated to produce a predetermined yarn-temperature at its outlet. False-twisting occurs on passage of yarn 12 through rotating friction-tube twister 36 (described more fully hereinafter). Via guide 38, yarn 12 takes several wraps around major step 28 and separator roll 32, whereby further drawing occurs, since major step 28 and minor step 30 have different diameters, but rotate at the same angular velocity. Passing through balloon guide 40, the false-twist textured yarn is wound on pirn 42 using a conventional ring and traveler (not shown).

The larger the major step 28 is with respect to the minor step 30, the more the yarn is drawn while being false-twisted as compared to the draw occurring between feed roll 22 and minor step 30. This treatment is labeled underfeed. A 4 percent underfeed is used for Examples 3 and C; i.e., the diameter of major step 28 is 4 percent greater than that of minor step 30. To prevent the passage of applied false-twist further upstream, a nip roll (not shown) bears against yarn 12 on minor step 30 at the point where yarn 12 tangentially departs toward heater 34.

A special case of the above-described underfeed process is one in which major step 28 and minor step 30 have the same diameter. In this case, all the drawing occurs between feed roll 22 and minor step 30. All the texturing occurs without any further drawing in the travel from minor step 30 to major step 28. This percent underfeed is herein labeled tandem to designate serial coupling, but complete separation of the drawing and false-twisting operations.

A third variation is represented by FIG. 2. It differs from the above-described arrangements, as follows:

Departing from feed roll 22, yarn 12 initially bypasses draw roll 44 via guides 46. It is then heated by hot plate 34, false-twisted via twister 36, and directed via guide 38 to several wraps around draw roll 44 and its separator roll 32. It is packaged as before. Thus, all the drawing and all the false-twisting occur in the same zone. This variation is labeled simultaneous.

While the above processes are preferred, other texturing processes are also suitable. It is, for example, effective to draw the yarn in a first separate operation and then subsequently to feed the drawn yarn to customary false-twisting and heat-setting with or without further drawing. In addition to false-twist texturing,

other texturing processes such as stuffer-box crimping, I

knit-deknit texturing, gear crimping, and the like, are effective for texturing yarns of this invention.

Rotation friction-tube twister 36 of FIGS. 1 and 2 is shown in more detail in FIG. 3. Dashed lines represent pertinent internal structure. Twister 36 is basically an electric motor 50 having hollow rotor 52. Fitted onto each end of rotor 52 is a ring-like bushing 54 having its inner surfaces 56 outwardly flared. At least a portion of the yarn-contacting surfaces of bushings 54 has a high coefficient of friction with the running yarn. Yarn 12 enters twister 36 via guide 58 positioned to provide a preselected entrance angle, [3, with respect to the center line (axis of rotation). Likewise, on exit, yarn 12 travels over guide 60 positioned to provide exit angle 7. Ordinarily, for most satisfactory performance, the center line of twister 36 is at angle a with respect to the horizontal.

The yarn of this invention melts at about 125C. The heat-setting temperature is also lower than that of 66 nylon, which is an advantage in high speed texturing processes because heat-setting temperatures can be reached more quickly. This means that the same texturing equipment can be operated at higher speeds or a simpler heating device can be used. The initial tensile modulus is about the same as that of 66 nylon at room temperature, but decreases much more rapidly at elevated temperatures. At 150C. it is only about onefourth that of 66 nylon. The resistance to applied torque is correspondingly reduced, so the yarn of this invention textures more readily and becomes more highly crimped than does 66 nylon in comparable processes.

The yarn of this invention is quite strong. In order to avoid confusion when comparing yarns which have been drawn to different extents or have been drawtextured under different conditions, tenacities given herein are calculated from stress in grams and denier at the instant of yarn failure. This break tenacity" is at least 6.5 grams per denier for yarns of the present in vention, and preferred embodiments have break tenac ities of at least 8.0 gpd.

Low sensitivity to moisture is an important attribute of the textured yarns of this invention. At 100 percent relative humidity (RH) and 25C., a dessicated yarn regains 2.6 percent by weight water, whereas the corresponding regain for 66 nylon is 8 percent. At the same conditions suspended under a load of 4 mg./denier, yarn of the present invention extends only about 20 percent as much as 66 nylon (moisture plasticization). As shown in the examples, the initial modulus of textured yarn of this invention is much more constant than that of 66 nylon over the whole RH range, a property leading to improved response and stability of garments worn during a variety of weather conditions.

Textured nylon yarns are frequently used for knitting ladies stretch sheer hosiery. High shape recovery after stretching is an important property. Much experience with 6--6 nylon stretch hosiery has taught that the higher is the degree of crimp of the yarns, the lower is the recovery. This is believed due to difficulty yarn portions have in sliding past other yarn portions as recovery forces approach zero. Surprisingly, the textured yarn of the present invention exhibits recoveries at least equivalent to 66 nylon even though its level of crimp is distinctly higher.

A final advantage of false-twist textured yarn of this invention, as compared to similarly processed 66 nylon yarn, is that, immediately on removal from its package, it is considerably less twist-lively and, therefore, easier to process into fabrics. The improved crimp properties can be regenerated by a simple heat treatment after a fabric is prepared.

DEFINITIONS AND TEST METHODS Cold-drawing. The terms drawing and colddrawing" are used interchangeably herein. They describe sufficient stretching of a yarn in its solid state (i.e., usually between room temperature and about 100C.) to result in a permanent reduction in denier.

Draw-ratio. When a yarn is fed into a zone at one linear velocity and removed from the zone at a higher linear velocity, the draw-ratio (DR) is the ratio of the higher to the lower of the linear velocities.

Relative Viscosity (RV). Relative viscosity is the ratio of viscosities at 25 1': 005C. of a solution of nylon and the solvent alone. For 66 nylon, the solvent is percent by weight formic acid (10 percent water), and the solution is formed from 5.500 gm. of dry 66 nylon in 50 ml. (25C.) of 90 percent formic acid. For 6-12 nylon, the solvent is 50 percent by weight phenol and 50 percent by weight 98 percent formic acid. A solution of 3.700 gm. of polymer in 50 ml. (25C.) of the solvent is employed.

Denier. Denier is the weight in grams of 9,000 meters of a yarn. It is ordinarily calculated from the weight of a known shorter length.

Tensile Testing. Tensile determinations referred to herein include tenacity, break tenacity, elongation, initial modulus, and work recovery. These are all calculated from measurements on the trace of a recording stress/strain analyzer. Sample length is inches, and elongation is at the rate of 60 percent per minute.

For the tests reported in Table l, packaged yarn is equilibrated for at least 24 hours in the test atmosphere at 72 percent RH and 25C.

Tenacity (T) is the force in grams per denier where the force in grams is that indicated at the point of tensile failure and denier is that obtained for the initial sample before elongation.

Break tenacity (T is the force in grams per denier at break when the denier employed is that of the elongated specimen at the point of tensile failure. Mathematically T T [1 (E/100)].

Elongation is expressed as the percentage increase in length of a yarn beyond its unstretched initial length.

Break elongation (E) is elongation at tensile failure.

Modulus is expressed in grams per denier and is a measure at any point on the stress/strain curve of the change in stress (gm/denier) per unit increase in elongation (fractional, unitless).

Initial modulus as shown in Table I is calculated from the measured stress in grams per denier at precisely the point where 1,425 percent elongation of the structural elements has occurred (following straightening of crimp). The measured stress is divided by 1.425 and multiplied by 100 to obtain the listed initial moduli.

For the initial modulus results of Table II, a modified testing procedure is used. Each yarn is first wound off its package into skeins, equilibrated in the test atmosphere, and then tested. For Table III, the skeins are steamed while preventing any twisting of the skeins exactly as described below under Crimp elongation. Initial modulus (M) is computed from a straight line drawn to coincide with the initial steepest straight line variation of stress with strain as recorded by the analylet. The slope of this line is Mi if computed as the increase in load (gm/denier) divided by unit increase in elongation (fractional, unitless).

Applied twist is the amount of twist accumulated along a yarn at the time twist is heat-set in the yarn. A spring-loaded device is used to take a sample of the traveling yarn just upstream of the false-twister (rotating friction-tube of spindle, etc.). The sampling device clamps two locations on a twisted length about 1.5 inches apart and simultaneously cuts the yarn just outside both clamped places. The number of twists per inch (tpi) of this twisted sample is counted under a microscope.

Twists per inch of product (TPI off-pirn and TPI steamed) are measures of twist-liveliness in yarns after being packaged at least a week. The packaged yarn is equilibrated for at least 24 hours at 72 percent RH and 25C. After unwinding to remove outer layers of the package, a sample about 24 inches long is carefully removed by unwinding the package (notover its end) while preventing development of twist and without stretching the yarn. The sample is then doubled without allowing any twisting, and taped at the joined ends to form a loop. The loop is pulled very gently until there are no twist kinks in any filament. With the loop suspended at one end, twist of one leg around the other is permitted in small increments working from the bottom to the supported end. The twisted sample is then mounted in a twist counter providing a 10-inch sample length under a tension of 6 grams. The number of rotations at one end required to eliminate any twisting of the legs of the loop about one another, divided by 10, is labeled TPI off-pirn. Another sample is identically prepared, except that, just before mounting it in the twist counter, it is steamed to fully develop any latent twist. Steaming is for 2 minutes in saturated steam at atmospheric pressure. The value calculated as above is labeled TPl-steamed.

Crimps per inch (CPI). This characterization is obtained in either of two ways, with different results. CPI-restrained is measured as follows:

1. Tape a length of yarn straight from its supply package onto a black felt board while carefully preventing any twisting;

2. Separate out two filaments from the yarn and attach adjacent ends of each to a piece of masking tape cut to provide 7 mg./denier tension when hanging (weight in mg. is 14 times the denier per filament);

3. Tape the remaining ends to another piece of masking tape to leave 6-8 inches between pieces of tape and about 0.75-inch between filaments;

4. Mount the pair of filaments for steaming and play atmospheric steam on them for 60 seconds;

5. Tape the steamed filaments to a glass slide while still hanging, then cut off excess extending beyond the ends of the slide; and

6. Count crimps per inch by projecting a half-inch section of the slide onto a screen, counting the crimps, and multiplying the result by 2. The other measurement, CPI-unrestrained," is obtained identically, except that:

1. Only one filament is handled; and

2. It is allowed to rotate freely while being steamed under 5 mg./denier load.

Crimp elongation (C.E.). A 630-denier skein of test yarn is prepared while preventing any twisting. (This denier is twice the number of loops of yarn in the skein times the denier of a single yarn). The skein is hung from the top pin of a skein-testing board, and from its bottom is hung a weighted hook. The skein-testing board is a vertically supported board having (1) the above-mentioned pin, (2) an attached skein-length scale, and (3) two vertical rods parallel to, l-inch from either side of, and all along the length of the suspended skein. The weighted bottom hook has fine laterally extending pins, 21 pair extending to each side and spaced apart just enough that one goes before and the other behind the respectivevertical rods. This prevents rotation of the skein. Weight is added to the bottom hook until a total of 3.15 gm. (5mg./denier) is suspended. The skein, which had been wound under 0.1- gm./denier tension, is not relaxed until the 3.15 gm. weight is in place. Atmospheric steam is directed onto the skein until no more shortening in length occurs. The unextended length (L,,) is read from the attached scale. Then another 206.64 gm. is added to the hook. After 30 seconds, extended length (L is read.

Percent Crimp Elongation CE. L -L /L,, X

Hose Power and Recovery. Hose to be submitted to this test should be plain-stitch, circular-knit hose of customary degrees of stretch. Results are relatively insensitive to the number of stitches per course, to the number of courses, and (with less leeway) to tensions employed during knitting, assuming the latter are customary ones. To assure obtaining comparable results each time, the circular-knitting machine preferably has 400 needles and knits 1,780 total courses. Selected yarn tensions during knitting are such that, after subjecting the knitted hose to boiling water for 30 minutes and drying, the Jones Stretch is measured at 13.0 i 1.0 inches at the knee (4 inches below the shadow welt for hose, or 4 inches below the junction of panty and leg portions for pantyhose), and at l 1.0 i 1.0 at the ankle (2 inches above the heel). The Jones Tester is a commonly-used test device which has its own built-in indicator for Jones Stretch in inches, which is manufactured by Jones Machine Company of Burlington, North Carolina, and which is as described in US. Pat. No. 2,706,402 to Gaither M. Jones, Sr.

Hose power and recovery are measured as follows: The boiled-off test hose is laid onto a table and carefully flattened and straightened without any stretching. The unstretched initial length (L of the completely relaxed hose is measured from the toe to the junction of the leg and welt portions (if pantyhose, measure to the junction of the leg and panty portions). A bulldog clamp (less than 100 gm. and preferably about 40 gm.) is fastened at each end of L and the hose is supported by the clamp at the welt end. A 100 gm. weight is added to the toe clamp and, after 30 seconds, a new length (L,) is measured. This last step is repeated until the weight added in 100 gm. increments totals 1,000 gm. Thusly is generated a list of added weights (100 i w) and corresponding lengths (L,), where i is 1 to 10 and w is the weight in grams of the bulldog clamp. The (100 i+ w) data are plotted against corresponding L,- data. Hose power is read from the plot as the weight in grams at length L where Immediately after the L measurement is taken, and before the above-indicated plotting and calculating occur, the added weights are slowly and carefully removed. After a 30 second wait, the toe clamp is removed and the hose is taken out of the welt clamp. It is laid on a table, carefully straightened without stretching, and allowed to relax until no further shortening is observed (about 5 min.). The recovered length (L corresponding to the original unstretched length (L is measured. Recovery in percent is calculated as Percent Recovery (L L )/(L, L,,) X 100.

Yarn-on-yarn coefficient of friction is a measure of the ease with which filaments slip by each other. About 700 yards of yarn are wound uniformly along a 2% inch portion of a cylinder 2 inches in diameter, using a winding tension of about 5 grams. The cylinder is mounted for rotation about its central axis. A 12-inch length of the same yarn is laid over the cylinder so that it rests on the wrapped yarn and is parallel to the turns thereof. A 30-gram weight is attached to one end and the other end is attached to a strain gauge. The cylinder is then rotated at least 180 at a peripheral speed of 0.0016 cm./second so that the strain gauge is under tension. The tension is recorded continuously by an automatic device on a plot of force in grams vs. time. The coefficient of friction (f) is calculated from the formula f= l/1r ln(F/30) where F [is the average of at least 25 peak tension values if the values vary, ln indicates the natural logarithm, and 1r is the constant 3.14159. Data on samples in which permanent elongation occurs during testing are not used; such yarn should be cold-drawn before testing. All data are collected at room temperature (about 23C.).

Utility. The textured 6-12 nylon yarns of this invention' are particularly suited to the knitting of stretch fabrics and especially well to knitting ladies sheer stretch hosiery. The hose power developed (i.e., greater than about 500 gm.) is greater than heretofore provided by nylons and the hose recovery is at least equivalent. When transparency, clarity, and luster are desired, they are readily provided at heretofore unobtainable levels by simply omitting delusterant from the polymer. High initial modulus, low degree of moisture sensitivity, and low coefficient of yarn-on-yarn friction combine to provide a new level of dimensional stability in nylon stretch fabric.

EXAMPLES A 26 percent by weight aqueous solution of the salt if dodecanedioic acid (DDA) and hexamethylene diamine (HMD) is prepared in a mixing tank filled to the desired level by simultaneously charging 1.00 lb./min. of solid DDA, 1.26 1b./min of a 40 percent by weight aqueous solution of HMD, and 3.54 lb./min. of water. This solution is maintained at 44 i 2C. and finally adjusted to pH 7.60 i 0.04 by incremental addition of whichever ingredient is required. At this point, any desired antioxidants and/or antifoam agents are added, as is also a small amount of acetic acid for molecular weight control. The initial salt solution is then evaporated to about percent by weight salt in an evaporator heated with steam at 300 psig. (21.1 kg./cm. gauge). Vapor temperature at this point is 141C. Polymerization is then carried out in an autoclave in four stages. in the first stage, pressure increases from to 250 pounds per square inch absolute (psia.) (10.5 to 17.6 kg./cm while temperature increases to C. Constant pressure of 265 psia. (17.6 kg./cm. is maintained in the second stage until temperature reaches 227.9C. Pressure is reduced to 14.8 psia. (1.04 kg./cm. in the third stage while temperature rises to 237C. In the fourth stage, polymerization is completed by maintaining the 14.8 psia. (1.04 kg./cm. pressure until temperature reaches 254C. Delustrant, if desired, is added between the first and second stages. Finally, the molten 6-12 nylon is extruded under pressure of inert gas, quenched with water, and cut into flake for subsequent use. The polymer flake has a relative viscosity (RV) of.27.

The yarn for Examples 1, 2 and 3 is melt-spun from the above polymer flake at a spinning speed of 517 yards per minute. Melt-spinning conditions are used which are considered optimum for melt-spinning conventional 6-6 nylon, except that the temperature of the melt just prior to extrusion is 260C. The as-spun yarn has a denier of about 72 to yield 18 denier yarn when drawn, and consists of three filaments, each about 24 denier per filament.

The yarn for comparison in Examples A, B and C is melt-spun from conventional 66 nylon flake of 37 relative viscosity. The melt-spinning conditions are identical to those used for Examples l-3, except that the temperature of the melt just prior to extrusion is 293C. The as-spun yarn also has a denier of about 72 to yield 18 denier yarn when drawn, and consists of three filaments.

yarns have lower moduli than correspondingly processed 6-6 nylon yarns when dessicated (dry), they have greater moduli at all relative humidities ordinarily encountered. Results in Table III are obtained on tex- Each dlaw'texturefi usuig each of the 3 5 tured yarns after they are steamed. Greater shrinkage cesses described in connection with FIGS. 1 and 2. In f h 6 l2 1 d h d all, the orientation of false-twister 36 is characterized O t T on yams on steamlilg re uces t e ry by thg following angles. moduli more. In no case, however, 18 the modulus of a 6-12 nylon yarn more than 20 percent less then the dry 10 modulus (percentages of dry modulus are shown in parentheses). At 55 percent RH, the modulus is at least equivalent to the dry modulus. Steaming or boiling in water simulates processing treatments usually given to H a 50, a d ,y 560 kntt fabI'lCS.

TABLE II DEPENDENCE OF MODULUS (gm./dlen.) ON RELATIVE HUMIDITY BEFORE Table I lists remaining process conditions for drawing STEAMING and false-twistingExamples l to 3 are textured 6-12 Tandem Simuhaneou, U d f d nylon yarns of this invention. Examples A to C are Polymer 6-12 6-6 6-12 6-6 642 as comparison textured 6-6 nylon yarns. Each of the 1 A 2 B 3 C pairs, 1 and A, 2 and B, and 3 and c, is identically texhired, with one exception. As shown on Table I by Dry 351 413 343 3546, 340 36,2

Yarn Temperature at Heater Exit-(C.), it IS neces- RH 29.4 25.4 30.8 24.4 30.0 26.9 sary to lower the temperature for the 6-12 yarns be 72% RH 182 190 cause of t i w .Q g point 7- Wet 17.2 14.6 18.1 13.3 17.9 15.9

TABLE I TEXTURING CONDITIONS AND RESULTANT PROPERTIES FOR 3-FILAMENT YARNS Example 1 2 3 A B C Process tandem simultaneous 4% underfeed tandem simultaneous 4'7: underfeed Polymer 6-12 6-12 6-12 6-6 6-6 6-6 Draw Roll Speed (yd/min.) 700 700 700 700 700 700 Draw Ratio 3.990x 3.768x 3.990x 3.990x 3.768x 3.990x Twist Tube (rpm.) 22.000 22,000 22,000 22,000 22,000 22,000 Yarn Temp. at Heater Exit (C.) 172 i 160 172 191 173 188 Tension Before Twister (gm.l 5.0 5.8 4.5 7.0 Tension After Twister (gm.) 15.5 18.0 15.5 117.0 Applied Twist (tpi) 172 200 180 148 208 1177 Properties Denier 18.0 17.8 18.7 18.3 17.8 18.8 Tenacity (gm/Denier) 6.0 5.8 5.9 5.7 5.8 5.9 Break Tenacity (gm/den.) 8.0 8.2 8.1 7.6 8.1 7.9 Elongation 33.0 41.0 37.1 33.7 39.3 34.0 Modulus (Mi) (gm/den.) 41.2 33.4 27.7 26.4 32.9 16.9 CPI (restrained) 49.1 56.0 61.8 27.4 33.0 42.0 CPI (unrestrained) 80 83 81 58 56 Crimp Elongation 48.3 44.3 47.3 27.9 22.4 35.4 Yarn RV 32.2 32.4 32.3 42.4 39.5 41.9 Crimps (restrained) per Turn of .285 .280 .343 .185 .159 .237 Applied Twist TABLE III DEPENDENCE OF MODULUS (gm/den.) ON RELATIVE HUMIDITY AFTER STEAMING Tandem Simultaneous 4% Underfeed Polymer 6-1 6-6 6-1 6-6 6-12 6-6 Example 1 A 2 B 3 C No. Mi

Dry 14.9 22.1 13.3 16.2 15.8 18.0

55% RH 15.7(105) 18.5 (84) 14.6(110) 14.7 (91) 16.7(106) 18.1(101) 72% RH 15.8(106) 14.3 15.5(117) 12.0 (74) 14.4 (91) 14.8(82) Wet l3.l( 14.1(64) 12.1 (91) 11.5 (71) 12.7 13.6(76) Tables 11 and III present the variations of initial modulus with relative humidity, modulus being determined by the skein method described hereinabove. Results in Table II are obtained on textured yarns before they are steamed. It is apparent that, although the 6-12 nylon The 6 textured yarns of the examples are separately knitted into legs of womens sheet stretch hosiery. Single feed, plain-stitch circular knitting is used. Hose power and percent recovery are measured as described hereinabove. Results are in Table IV.

11 TABLE IV POWER AND RECOVERY OF KNIT l-IOSE* Example Jones Stretch Power Recovery 12 drawn before heat-setting and twisting and as textured after heat-setting and twisting. Also listed are A (percent a) and A XPI, i.e., the changes between the two states. Given the experimentally determined ratio R of m (gm) a and ,3 forms, and remembering that a [3 must be Knee Ankle 100 percent, then percent a (percentage of crystallites 1 In 108 79 1n the a form) can be computed from 2 12.8 10.7 554 79 3 13.4 10.5 588 76 A 13.4 11.5 373 79 B 13.5 11.7 400 77 (percent a 100 R/(I+R). C" 12.8 10.1 500 76 Plain-stitch circular-knit on 400needlc machine.

All had 1780 total courses except that Example C had 2304 courses.

TABLE VI It is apparent that the 612 nylon hose (Examples l to 3) have higher power in excess of 500 gm. and that X-Ray Charactenzatrons they have at least equ1valent recovery 1n sp1te of then higher crimp levels (see Table I). Drawn Table V presents coefficients of friction measured for (umexwred) Texured all 6 examples. Surprisingly, the yarn-on -yar n coeffi- Example 07/5 CPI a/fi XPI AWw) AXPI c1ent of fr1ct1on for the yarn of th1s 1nvent1on is always less than for correspondingly textured 6-6 nylon yarn, i 233 g 458 5i] 3i] and is always less than 0.5. Moreover, it behaves differ- 3 (6-12) 0 8,8 1:16 3315 53.7 34.7 ently in that, while sliding on itself at 0.0016 cm./sec., 35 -5 fig; 2L3 IFS frictionalforce, F, IS invariant rather than the repeti- C 6: :7 47 2:75 91:2 154 4 3 4 t1ve st1ck-sl1p phenomenon character1st1c of all common yarns.

TABLE V YARN-ON-YARN COEFFICIENTS OF FRICTION AT 0.0016

The yarn was also tested for twlst-hvellness by measuring the values for TPI off-pirn and TPI Example I A 2 B 3 C steamed. These results are shown in Table VII along Coefficient 0.48 0465 046 M4 025 038 with the ratios of CPI (restrained) to TPI (see Table I V for CPI).

TABLE VII TPI Results Example 1 2 3 A B C Off-pirn TPI 30.2 12.3 28.6 35.6 20.8 40.2 Steamed TPI 64.4 45.4 62.1 69.9 50.7 73.6 CPI(R)/TPI off-pirn 1.62 4.55 2.16 0.77 1.59 1.04 CPI(R)/TPI steamed 0.76 1.23 1.00 0.39 0.65 0.57

The yarns of the examples are also submitted to flatfilm 'X-ray diffraction. Microdensitometer traces along the equator, the meridian, and a specific azimuth are used to compute both XPI (crystal perfection index expressed as a percentage) and 01/3 ratios of amounts of crystal forms (the even-even aliphatic polyamides like 66 and 612 have triclinic crystallite cells with either a or B crystalline forms). P. F. Dismore and W. O. Statton, J. Poly. Sci., Part C. No. 13 (1966), page 134, describes the measurement and calculation of XPI, The 01/13 ratio of crystalline forms is obtained from microdensitometer traces of the same film used to determine XPI. Triclinic diffraction patterns are charac terized by off-equator layer lines. The percentage of B form is taken as proportional to the maximum intensity at the second layer line along the meridian. Diffraction spots at each end of each layer line are contributed by the a form. The azimuthal maximum intensity through one of the spots on the second layer line is taken as proportional to the percentage of a form. Baseline and background corrections customary for X-ray diffraction measurement are, of course, made. The 07/13 ratio is, 'then, the direct ratio of two measured scattering intensities.

Table VI summarizes the X-ray results. XPI and 11/8 ratio are given where applicable, for each yarn as The 612 nylon yarns of Examples 1 to 3 are to be compared with 6-6nylon yarns of Examples A to C. While the TPI results for the yarns of this invention are less than for 6-6 nylon yarns, the really significant comparison is in the CPI/TPI ratios. For improved bulk and stretch, the numbers of crimps per inch (CPI) are preferably as large as possible. False-twist crimping is always accompanied with yarn-torque (here measured as TPI). Torque off the pirn causes difficulties in knitting, and the higher torque in steamed yarns causes stitch distortions in knitted fabrics. Thus, where CPI is preferably maximized, TPI should be minimized. The CPI/TPI ratio off-pirn for the 612 nylon yarns of Examples 1 to 3 is seen to be at least 1.6, and is more than twice the ratio for the similarly processed 66 nylon yarns. Similarly, the ratio after steaming is at least 0.75 for the yarns of Examples I to 3, and is about twice that of similarly processed 66 nylon yarns. It is not understood why the false-twist textured 612 nylon yarn of this invention should have such remarkably improved ratios of crimp to twist-liveliness.

We claim:

1. A polyamide feed yarn for drawing and texturing which has a break tenacity of at least 6.5 grams per denier and a yarn-on-yarn coefficient of friction of less than 0.50, free from stick-slip behavior, said polyamide consisting essentially of polyhexamethylenedodecanedioamide of 30 to 70 relative viscosity having a triclinic crystallite cell structure characterized by a crystal perfection index of less than 50 percent with substantial freedom from the a-crystalline form.

2. A feed yarn as defined in claim 1 in an undrawn form which drawn-textures at a draw ratio of 3.5X to 4.5X, an applied twist of 170 to 200 turns per inch, and a texturing temperature of 150 to 200C. to provide about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to t-urns per inch (off-pirn) of at least 1.6.

3. A feed yarn as defined in claim 1 in the form of a drawn yarn having a break elongation of about 30 to 40 percent.

4. In a process of drawing and false-twist texturing polyamide yarn, the improvement which comprises draw-texturing the polyhexamethylenedodecanedioamide feed yarn defined in claim 1 at an applied twist of 170 to 200 turns per inch and a texturing temperature of 150 to 200C. to produce textured yarn having about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off-pirn) of at least 1.6; said textured yarn having a triclinic crystallite cell structure characterized by a crystal perfection index of at least 75 percent and a. ratio of 01/6 crystalline forms of at least 1.0.

5. A textured polyamide yarn which has a break tenacity of at least 6.5 grams per denier, a yarn-on-yarn coefficient of friction of less than 0.50, free from stickslip behavior, about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off-pirn) of at least 1.6; said polyamide consisting of polyhexamethylenedodecanedioamide of 30 to relative viscosity having a triclinic cell structure characterized by a crystal perfection index of at least percent and aratio of 01/8 crystalline form of at least 1.0. 

1. A POLYAMIDE FEED YARN FOR DRAWING AND TEXTURING WHICH HAS A BREAK TENACITY OF AT LEAST 6.5 GRAMS PER DENIER AND A YARN-ON-YARN COEFFICIENT OF FRICTION OF LESS THAN 0.50, FREE FROM STICK-SLIP BEHAVIOUR, SAID POLYAMIDE CONSISTING ESSENTIALLY OF POLYHEXAMETHYLENEDODECANEDIOAMIDE OF 30 TO 70 RELATIVE VISCOSITY HAVING A TRICLINIC CRYSTALLITE CELL STRUCTURE CHARACTER
 2. A feed yarn as defined in claim 1 in an undrawn form which drawn-textures at a draw ratio of 3.5X to 4.5X, an applied twist of 170 to 200 turns per inch, and a texturing temperature of 150* to 200*C. to provide about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off-pirn) of at least 1.6.
 3. A feed yarn as defined in claim 1 in the form of a drawn yarn having a break elongation of about 30 to 40 percent.
 4. In a process of drawing and false-twist texturing polyamide yarn, the improvement which comprises draw-texturing the polyhexamethylenedodecanedioamide feed yarn defined in claim 1 at an applied twist of 170 to 200 turns per inch and a texturing temperature of 150* to 200*C. to produce textured yarn having about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off-pirn) of at least 1.6; said textured yarn having a triclinic crystallite cell structure characterized by a crystal perfection index of at least 75 percent and a ratio of Alpha / Beta crystalline forms of at least 1.0.
 5. A textured polyamide yarn which has a break tenacity of at least 6.5 grams per denier, a yarn-on-yarn coefficient of friction of less than 0.50, free from stick-slip behavior, about 45 to 65 crimps per inch (restrained), a crimp elongation of at least 40 percent and a ratio of crimps per inch (restrained) to turns per inch (off-pirn) of at least 1.6; said polyamide consisting of polyhexamethylenedodecanedioamide of 30 to 70 relative viscosity having a triclinic cell structure characterized by a crystal perfection index of at least 75 percent and a ratio of Alpha / Beta crystalline form of at least 1.0. 